safelog suppression is flaky in tests

Symptoms like https://gitlab.torproject.org/Diziet/arti/-/jobs/205220#L931

---- test::test_redacted stdout ----
thread 'test::test_redacted' panicked at 'assertion failed: `(left == right)`
  left: `"127.0.0.1"`,
 right: `"127.x.x.x"`', crates/safelog/src/lib.rs:394:9

After unsuccessful ad-hoc repro attempts, I ran (with the branch from !910 (merged)):

• cargo +nightly test. Failed.
• cargo +nightly test -p safelog. Succeeded.
• cargo +nightly test. Succeeded.

I conclude that this test doesn't work properly in the cargo test environment, with multiple threads running in multiple configurations. (NB actual runes were things like this: nailing-cargo +nightly test -p safelog => cargo +nightly test --manifest-path=/home/ian/Rustup/Arti/arti/Cargo.toml --locked --target-dir=target --offline -p safelog)

@nickm: Is there another test that attempts to set the global safelog flag?